Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual dezembro tem um recorde de 21-6-5?
 ###Tabelas: CREATE TABLE doubles_20_10-10 (doubles_20_10-10_id AUTO_INCREMENT PRIMARY KEY, Outcome VARCHAR, Date VARCHAR, Tournament VARCHAR, Surface VARCHAR, Partner VARCHAR, Opponents in the final VARCHAR, Score VARCHAR) CREATE TABLE regular_season (regular_season_id AUTO_INCREMENT PRIMARY KEY, Game INT, December INT, Opponent VARCHAR, Score VARCHAR, Record VARCHAR, Points INT) CREATE TABLE parliamentary_elections (parliamentary_elections_id AUTO_INCREMENT PRIMARY KEY, Election INT, Number of PNC votes VARCHAR, Share of votes VARCHAR, Seats VARCHAR, Outcome of election VARCHAR) CREATE TABLE careers (careers_id AUTO_INCREMENT PRIMARY KEY, Career Card VARCHAR, Starting career/salary VARCHAR, 2nd career/salary VARCHAR, 3rd career/salary VARCHAR, 4th career/salary VARCHAR, 5th career/salary VARCHAR, 6th career/salary VARCHAR) CREATE TABLE finals_champions_league_era (finals_champions_league_era_id AUTO_INCREMENT PRIMARY KEY, Season VARCHAR, Winner VARCHAR, Score VARCHAR, Runner-up VARCHAR, Losing Semifinalists VARCHAR)  
SELECT AVG December FROM regular_season WHERE Record = 21–6–5